<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box2 {
      width: 200px;
      height: 180px;
      background-color: blue;
      /* border: 1px solid transparent; */
      /* padding-top: 20px; */
      /* overflow: hidden; */

    }

    .box2 p {
      width: 100px;
      height: 100px;
      background-color: #fff;
    }
  </style>
</head>

<body>
  <!-- 塌陷 -->
  <div class="box2">
    <p>1</p>
  </div>

</body>

</html>